Differential amplifiers are widely used in electronic circuits for such applications as voltage comparators, detector circuits, analog-to-digital conversion circuits and differential receivers. Heretofore a primary limitation on the operation of many differential amplifiers has been that the input voltages are constrained to operate in a region approximately halfway between the voltages at the power terminals which supply power to the differential amplifier. In general, as the voltages on the input terminals approach the supply voltage, the operation of a differential amplifier becomes degraded or terminates completely. Operation of a differential amplifier with input voltages above the supply voltage is difficult. This can be generally be carried out only with the use of voltage divider and voltage reduction circuits which buffer the input voltages to the differential amplifiers.
In view of the above limitations, there exists a need for a differential amplifier which functions when the voltages on the input terminals equal or exceed the supply voltage as well as when the input voltages are less than the supply voltage.